This invention relates to reciprocating machines such as pumps, compressors and engines and in particular is directed at boundary or interface components for effective high pressure, high efficiency operation of reciprocators.
These boundary or interface components are preferably used in an internal combustion engine of the type described in the application of Paul, Ser. No. 805,184 filed Dec. 5, 1985, entitled, Regenerative Thermal Engine. In that application engine designs were presented enabling peak cylinder pressures up to 180 atmospheres. While such pressure is greater than the peak pressure of conventional engines, further increasing peak pressure will exceed known design limits for piston seals and rod pins and cause design problems for effective air charging of the combustion chamber. The invented improvements solve those problems and enable design limits of 200 to 300 bars to be achieved in a two cycle engine. Since these improvements, particularly the sealing and bearing improvements, solve boundary or mechanical interface problems, their application is not limited to hyperbar combustion engines. Applications extend to compressors, pumps and other machines, principally reciprocating devices, where a translation of linear and rotary motion occurs. The rigorous operating conditions of the internal combustion engine, however, provide the exemplary environment for description of the preferred embodiments. The reciprocator in the engine system described in this application is capable of achieving peak combustion pressures of 200-300 bars. At such pressures, conventional piston rings are squeezed outward in their groves and forced against the cylinder wall by the pressure of the combustion gases that seep behind the rings. For example, in a ring system having three staggered rings in three spaced grooves, a pressure equivalent to 80% of the combustion chamber pressure is developed behind the top ring, a 50% chamber pressure is developed behind the center ring and a 20% chamber pressure is developed behind the bottom ring. The forced expansion of the rings dramatically increases slide friction between the contact edge of the rings and the wall of the piston. In addition to excessive friction losses, excessive wear and scarring render conventional piston ring assemblies unacceptable for high pressure cylinder environments. Although the regenerative cylinder wall of the referenced application provides a labyrinth-groove type solution to the expanding ring problem, its use is most effective in high r.p.m. devices and is not entirely suitable for engines operating at low or variable speeds where positive sealing is preferred.
The ring assembly of this invention solves the problems of conventional rings and enables extremely high chamber pressures to be obtained by a positive seal ring system with minimal leakage and friction.
Maximizing peak combustion pressures substantially increases effective engine efficiencies, but has heretofore been limited by design considerations relating to the wristpin interconnecting the piston head and the connecting rod. The dual pin arrangement for the tandem connecting rod and double crank assembly of the referenced application improves the operating specifications for a pin design by sharing the load between two pins. However, further increasing pin size to distribute loads over a greater surface area is limited by the piston diameter and bearing structure necessary to accommodate and encompass the two spaced pins. Lengthening the connecting rod to reduce the component of side force on the wristpin increases the size of the engine and magnifies adverse inertial effects.
This problem is solved by the dual, interfacing wristpin assembly of this invention, which remarkably eliminates that portion of rotary slide friction generated by the side component of the thrust force during the power stroke. The dual wristpin thus increases the effective surface area for distribution of thrust forces and enables use of short connecting rods without increase in friction forces.
The third component for high pressure systems is a pressure equalizer. The equalizer or converter has application primarily in internal combustion engines. The pressure equalizer assembly comprises an interconnecting passage or channel between the exhaust conduit and the compressed air intake conduit with a displaceable barrier in the channel. In a high pressure two cycle reciprocator, intake air must be sufficiently pressurized to purge exhaust gasses. To assure that the pressurized intake air has at least reached the discharging exhaust pressure, cross-manifold devices have been developed, such as the COMPREX.RTM. pressure-wave supercharger that equalizes exhaust and intake pressures. In the Comprex an external power connection rotates a multivane rotor. The radial vanes are parallel with the axis of rotation in the manner of a paddle wheel. Discrete passages are formed between the vanes for the exhaust and air to meet, but not mix. Rotation allows a gradient to develop such that the lower pressure compressed air is raised in pressure and the high pressure exhaust is lowered in pressure as the vanes transport the gases from one radial position to another. Although suitable for a multi-cylinder engine where gas pressures are relatively stable, in a single cylinder engine pulsing problems require a different solution. The positive displacement floating piston equalizer divided herein effectively adapts the unique pressure balance concept of the Comprex to a monocylinder engine.